Especially in view of the increasing shortage of petroleum-based fuels and of natural gas fuels, the desirability has been recognized of being able to substitute for them other more available fuels such as particulate coal, sawdust, or other comminuted solid-fuel materials. However, different techniques are required for transporting and distributing the particulate fuel to the fuel burners, along with appropriate amounts of oxygen for accomplishing combustion, than are appropriate for oil and natural gas fuels, for example. A particular use for such particulate solid fuels is in the fueling of kiln furnaces used for the drying and/or firing of ceramic products such as bricks, for example, and it is with particular regard to such applications that the present invention will be described in detail.
It should be understood that in some applications, such as the kiln firing of bricks, it is desirable to supply the airborne particulate fuel from a single source to a plurality of burner ejectors, in controlled quantities and sequentially, so that the burner ejectors receive appropriate pulses of fuel at appropriately timed intervals, preferably together with enough primary air to effect the desired combustion of the particulate fuel in the furnace.
One form of apparatus which has been proposed for this purpose includes a rotary distributor of the air-borne particulate fuel, wherein the airborne particulate fuel is supplied from a single source via an inlet conduit to the distributor, with the aid of a blade-type suction fan or blower in the line between the source and distributor inlet. The distributor in that case comprised a stationary plate within a distributor housing, having a series of spaced openings extending through the plate and arranged in a circle, the outlet conduits for supplying the several individual burner ejectors extending from these openings to the respective ejectors. Within the distributor housing, an eccentric rotating distributor arm was arranged to communicate from the distributor inlet to each of the plate openings in sequence, by rotating it into alignment with them successively as the arm rotated.
Such a system has been found to have several practical drawbacks. Firstly, because the conventional suction blower is positioned so as to be traversed by the airborne particulate fuel, it is constantly subject to impingement by these particles and hence tends to deteriorate rather rapidly. Although one might use a blower on the upstream side of the point of injection of the fuel as a means of avoiding impingement of the blower by the fuel particles, the resultant substantial back-pressures and outward air flows thereby produced at the fuel inlet present difficulties in injecting the particulate fuel into such an airstream.
Accordingly, we have found it desirable to use a venturi type arrangement for the fuel injecting operation, which in effect sucks the particulate fuel into a high-velocity air stream and, since it has no moving parts and presents a very small profile to the stream of fuel particles, does not deteriorate appreciably or require maintenance each over very long periods of use.
When such a venturi-type ejector is utilized, it preferably provides two basic functions, namely, it accomplishes injection and transportation of the desired amount of fuel, and in addition supplies primary air mixed with the fuel in an appropriate amount to facilitate proper combustion of the fuel at the burner ejectors. It will be understood that the operation of the venturi-type device is affected by the back pressure exerted by the entire air-fuel transportation system between it and the ultimate burner ejectors. Accordingly, if the venturi ejector is used with the previously-known system described above, it may be possible to provide a system which will operate satisfactorily in one specific application to supply a specific size at a particular rate, but it has not been found practical to design such a system which will provide operation over a wide range of fuels, fuel sizes, fuel delivery rates and burner ejector arrangements.
As a further drawback of the above-described previously-known system, the type of rotary distributor used was in itself found to be less than optimum for its intended purpose. First, it tended to introduce substantial undesired back pressures due to its feeding of outlet supply conduits and burner ejectors of restricted cross-sections one at a time. Secondly, leakage of particulate fuel into the housing of the rotary portion of the system tended to produce an accumulation of such particulate fuel therein, requiring rather frequent servicing and cleaning. While it had been recognized that such leakage was normally accompanied by a small elevated air pressure in the housing which might tend to drive some of the accumulated fuel particles into those outlet conduits not then being fed by the distributor, and thus to exert some degree of cleaning action, it has been found that this is not adequate to prevent rather rapid undesired accumulation of fuel particles in the housing. Also, the eccentric rotating arm described above was awkward to mount, resulted in an unbalanced rotational load, and was mechanically undesirable for these reasons.
Further, we have found it advantageous to be able to supply controlled amounts of additional air to the furnace, independently of that which is provided by the venturi ejector. For example, we have found it desirable in some cases thereby to supply a substantial excess of air to the furnace beyond the stoichiometric amount which would be theoretically required for complete combustion, so as to provide the desired atmosphere in the kiln furnace. The above-described previously-known system and distributor does not accomplish this, and the air which it supplies to the furnace is merely that which the venturi can provide as a part of its fuel-ejecting action.
Accordingly, it is an object of the present invention to provide a new and useful rotary distributor of airborne particulate solid fuel, having certain improved characteristics.
It is another object to provide such apparatus having improved self-cleaning characteristics.
Another object is to provide such a distributor which does not present an unbalanced rotational load.
Another object is to provide a system using a rotary distributor in combination with a venturi device for supplying air-borne particulate solid fuel through the distributor to burner ejectors, which system is efficient, has long life, does not require frequent maintenance, and can be adapted to a wide range of applications.
A further object is to provide such a system and distributor in which controlled amounts of air in addition to that provided by the venturi ejector can be delivered to the furnace in controlled amounts by way of the distributor.